I've used both fairly extensively now and there are definitely pros and cons to each. I haven't done any solid benchmarking, but RS feels faster. It's also much easier/faster to get up and running whereas AWS has a bit of a barrier to entry. While at times I've been given incorrect info from them it's great to be able to get support staff on the live chat.
I wouldn't necessarily choose it for all applications though. The AWS architecture is far more flexible in general. Elastic IPs are invaluable when it comes to creating a system that can grow over time (seamlessly switch from a single instance to several fronted by a load balancer in a couple of minutes). Being able to take complete snapshots of your system on an hourly basis could well save your business one day. Being able to make a couple of API calls to attach an extra 1 TB drive to your instance? That's worth losing a little horsepower over.
It all depends on what you're after; with Rackspace you probably get a faster machines, but that's at the expense of being able to build a more robust generic solution for your needs.
I wouldn't necessarily choose it for all applications though. The AWS architecture is far more flexible in general. Elastic IPs are invaluable when it comes to creating a system that can grow over time (seamlessly switch from a single instance to several fronted by a load balancer in a couple of minutes). Being able to take complete snapshots of your system on an hourly basis could well save your business one day. Being able to make a couple of API calls to attach an extra 1 TB drive to your instance? That's worth losing a little horsepower over.
It all depends on what you're after; with Rackspace you probably get a faster machines, but that's at the expense of being able to build a more robust generic solution for your needs.